The Vote to Name Pluto’s New Moons

Pity poor Pluto. Once considered to be a full-fledged member of the planet club, it was officially relabeled as a dwarf planet in 2006. But it is, nonetheless, a fascinating celestial body—just ask Mark Showalter, a planetary astronomer at the SETI Institute, who in 2011 was leading a team to search for possible rings around Pluto. Using the Hubble Space Telescope, he discovered something new: a fourth moon, dubbed P4. A year later, with the safety of NASA’s approaching New Horizons spacecraft in mind (it will fly by Pluto in July 2015), a bigger effort was made to search for other moons, and voilà, a fifth one, called P5, was discovered. The two moons are part of a complex system: Pluto’s main moon, Charon, is about half its size and orbits every 6.5 days; the other three moons orbit the two inner bodies, making it, as Showalter points out, like a “binary planet.”

But what to name the new moons? Showalter decided to put it to a vote for the general public. Since Pluto (also called Hades) is the god of the underworld, the designations of its already-named moons are generally connected with that theme: Charon and Hydra are characters in Hades’s mythical realm; Nix is the night goddess, and in some versions of mythology, Charon’s mother. The list of possible names the public could vote on included such figures as Eurydice, Persephone, and Orpheus.

Enter William Shatner. The actor, famous for playing Captain Kirk on the original Star Trek series, suggested via Twitter that the two moons be called Vulcan and Romulus. Romulus was already taken, but there are no celestial bodies outside the Star Trek world that are actually called Vulcan.

“At first I thought this was kind of a frivolous idea—I mean, honestly, we’ve been getting all kinds of ridiculous ideas,” Showalter says. “We’re pretty sure we heard hundreds or thousands of nominations for Minnie and Mickey and Goofy and Dopey.” But the vote was always open to write-in nominations, and Showalter decided to add Vulcan to the list of possibilities. Vulcan is indeed the name of a Roman god, but doesn’t have an obvious connection with the underworld, and as the god of fire, might seem an incongruous fit in such an icy corner of the solar system. No matter. When the voting concluded February 25, Vulcan was far and away the winner, receiving more than 150,000 votes. The two runners-up were Cerberus and Styx.

Vulcan will not automatically become the name of one of Pluto’s two new moons, however. Showalter’s team needs to decide what two names to formally propose to the International Astronomical Union, the body that has the power to accept or deny them. In doing so, Showalter says they need to consider this question: “is Vulcan an appropriate name for a moon of Pluto?” He added that his “highest priority is that I want the public to feel like they really played a role in the naming of the moons of Pluto.” When accepting a name, the IAU must take into account multiple factors, including, in this case, whether the names are connected with Pluto’s mythology. With a name like Cerberus or Styx, says Rosaly Lopes, the chair of the IAU’s Outer Solar System Task Group, “there is a much more clear connection to Pluto.” As for Vulcan, she adds, that name “is a little bit more iffy. I like it because I’m a volcanologist—and a Star Trek fan—but we really need to look [at] whether it fits well.”